Interference of ISEcp1-bla_CTX-M-1 with the shufflon rearrangement in IncI1 plasmids

IncI1 plasmids are known disseminators of the extended-spectrum cephalosporin resistance (ESC) gene bla_CTX-M-1, among species of the Enterobacteriaceae family. In several IncI1 plasmids, this gene was found incorporated into the transposition unit, ISEcp1-bla_CTX-M-1-orf477, interrupting a shufflon region, a hallmark of IncI1 conjugative plasmids. The shufflon diversifies pilV gene that encodes the adhesine-type protein found on the tip of the conjugative pilus. To further elucidate the shufflon rearrangement, we examined to what extent the shufflon rearrangement was affected by the transposition-unit insertion. As expected, the interrupted shufflons generated a lower number of shufflon variants and exhibited an altered segment-deletion pattern compared to the non-interrupted shufflon. Interestingly, segment-loss frequency of the interrupted shufflons was distinctive in different plasmid hosts. Finally, the analysis of the 3' end of the pilV gene revealed that shufflon rearrangement favoured segment A to complete pilV partial open reading frame regardless of the shufflon. Thereby, it could be assumed that the A-segment has greater importance during conjugation, however, this remained a hypothesis. Further exploration of shufflon rearrangement and its importance in the plasmid-recipient selection during conjugation would be beneficial as the knowledge could be applied in developing a strategy to limit IncI1 mediated antimicrobial resistance dissemination.